Method of chemical testing of oils



Uite States atent 3,030,190 METHOD Gir CHEMICAL TESTENG F OILS Walter P. Seemann, Hamburg-Gr. Flottbek, and Harald Hellberg, Hambnrg-Poppenbuettel, Germany, assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Apr. 26, 1960, Ser. No. 24,685 Claims priority, application Germany May 25, 1959 8 Claims. (Cl. 2323il) The present invention relates to a method of chemical testing of oils and particularly to a rapid method of determining the neutralizationnumber of mineral lubricating oils, as a measure of the degree of aging or change in stability of the oil, and to an article of manufacture for determining the acidity of oils.

Itfis well known that in storage or during use various types of oils, such as mineral oils, tend to form or become contaminated with acidic materials. When the formation of these contaminants in a given oil is greater than a certain value the oil becomes acidic and in the case of mineral lubricating oils is the cause of wear and corrosion of engine parts.

The determination of the acidity which develops in oils has long been a difficult problem and very time-consuming. Measuring the neutralization number by standard U.S. methods such as the ASTM methods or the German DIN method requires laboratory facilities which are not practical for the average user of such products such as the gas station attendant or fleet operator for they generally lack time, training, and proper facilities for carrying out the standard procedure.

The neutralization number is a measure of the acidity and is defined as the number in mg. of KOH needed to neutralize the free acids in one gram of the material tested. According to the German method DIN 51.558 which is essentially equivalent to ASTM D664-58 method, the neutralization number is determined by weighing an oil sample, dissolving the sample in a solution of alkali blue 6B in an ethanol-benzene mixture and titrating the solution with N-alcoholic caustic potash solution until the blue color of the solution changes to red.

However, under what might be termed field conditions, as contrasted with laboratory conditions, it is often desirable to see at a glance the degree of aging of an oil. The determination of the neutralization number according to the above standard methods is normally limited to the laboratory and in addition is a very time-consuming and expensive operation.

A method has now been found which makes it possible to obviate the elaborate laboratory procedure and to determine the neutralization number rapidly and sutficiently accurately for the indicated purpose.

In accordance with the present invention, it has been found that the determination of the degree of acidity of mineral oils can be rapidly determined by use of a particular solid substance in tabletted form which is capable of neutralizing the acids present in the oil. The solid substance is an alkali metal salt of a nitrophenol having a dissociated constant of from 5.3 l0 to 10X 10- such as sodium or potassium m-nitrophenate. The compound preferably is monohydrate sodium m-nitrophenate (C H (NO )ONa-H O). A mixture of the sodium mnitrophenate and an inert carrier material is suitably so tabletted that each tablet contains 3.19 mg. of

which corresponds to an alkaline content of 1 mg. of KOH. It is also possible to produce tablets corresponding to a larger or smaller quantity of KOH, for instance 0.5, 2, 4, 5, etc. mg. of KOI-I. In practice, two types of tablets can be suitably used, viz., tablets corresponding to 5 mg. of KOI-I and tablets corresponding to 1 mg. of KOH, it being possible to produce the latter in such a way that they can be readily broken up into two equal parts. These tablets are new articles of manufacture and are easily and simply used for determining the neutralization number of oils in accordance with the present invention.

The inert carrier material for the alkali nitrophenate may be any solid hydrocarbon which is soluble in a suitable indicator of a mixture of alcohol and benzene solution, such as specified for example in the German method series DIN 51,558, Section 7.1.

The inert carriers may include solid hydrocarbons such as waxy materials, polyaromatics such as unsubstituted or alkyl-substituted naphthalenes, anthracenes or phenanthrenes, e.g., naphthalene, anthracene, phenanthrene, tetralin, decalin, chrysene, indene, C alkyl naphthalene, anthracene, and phenanthrene; phenanthrene has been found to be particularly suitable.

Indicators which are suitable for practicing the invention are any of the well known organic acid-base indicator compounds or any combination thereof, which change color in a desired pH range. Preferred indicators are those which develop strong colors, are stable in air for at least one or two minutes, and are not sensitive to short exposures to the small atmospheric concentrations of carbon dioxide.

Useful indicators may include a wide variety of compounds of which are preferred sulfonic acid derivatives or salts thereof, such as sodium salt of triphenyltriamino triphenylcarbinol sulfonic acid, sold under the trade name alkali blue 6B, p-benzene sulfonic acid-azo-alphanaphthylamine, 4-amino-l-naphthene-azo-benzene-4-sulfonic acid, etc.

To determine the neutralization number by the method of this invention a certain volumetric quantity of a test oil is introduced into the test vessel (the specific gravity of a mineral oil is approximately 0.9) and a solution of the indicator such as alkali blue 6B in an alcohol-benzene mixture added as specified by the German method DIN 51,558, Section 7.1. The amount of oil present in the solution mixture is not critical, the main requirement being that the oil should be completely dissolved in the solution and that the entire mixture be fluid. In general, about 5 to 10 ml. of oil to 20 to 40 ml. of indicator solution is desirable and practical. Preferably, the indicator solution contains about 0.3 mg. alkali blue 6B per ml., the ratio of alcohol to benzene being 2:3.

After addition of the alkali blue solution the tablets are added individually until the blue solution turns red. The test vessel is shaken after addition of each tablet and left to stand until the tablet disintegrates. When correctly tableted, the tablets disintegrate within 10-20 seconds, so that the neutralization number can be determined in the shortest possible time.

An illustration of the applicability and dependability of the present method is as follows: To a graduated flask, with a ground glass fitting, is added about 11 ml. (10 grams) of transparent oil, or 5.5 ml. (5 grams) if the oil is not transparent. The alkali-blue 6B solution as described above is added to the oil to a mark on on the vessel designated about 20 ml. The vessel is closed by means of a ground-glass stopper and shaken to dissolve the oil in the alkali blue solution. The required number of sodium m-nitrophenate tablets is added until the color change from blue to red is observed.

The neutralization number is calculated from the consumption of tablets.

Test 1 Vessel filled up to 5.5 ml. or approximately 5 grams of oil. After addition of 5 tablets (each corresponding 3 to 1 mg. of KOH) the solution was still blue; after addition of 5.5 tablets the solution was red. Hence the end point was therefore between and 5.5 tablets corresponding to a neutralization number between 1 and 1.1.

acidic substances and concomitant deterioration which comprises measuring a sample of the oil and dissolving it in an alcohol-benzene solution containing an indicator and dissolving therein the number of tablets having dis- Test 2 5 sociation constants of from 53x10 to 10X 10- of alkali nitrophenate until there is a visual color change. filled p I? 11 mL or pp y 10 grafns 2. The method of claim 1 wherein the tablets comprise of After addltlon f s (e h correspondms an admixture of an inert oil-soluble hydrocarbon solid 9 1 of the Solution was 1 blue, after add1- and the alkali nitrophenate is sodium m-nitrophenate. tlofilof tablets the 501M101! s Hence the end 10 3. The method of claim 2 wherein the inert oil-soluble point was somewhere between 4 and 4.5 tablets, correhydrocarbon olid is phenanthrene. P IIdmg to a neutralization number between 0.4 and 4. The method of determining the neutralization number of mineral oils which are subject to acidic substances Test 3 and concomitant deterioration which comprises measurvessel n up to 55 or approximately 5 grams l5 ing a sample of the oil and dissolving it in an alcoholof cm After addition of 7 tablets (each Corresponding benzene solution containing alkali blue 6B and dissolving to 5 of KOH) and 2 tablets (each Corresponding to therein the number of tablets of phenanthrene-sodium 1 mg. of KOH) the solution was still blue; after a fur m'xiltrophfinate the amount of P pres.ent being that. addition of 1 tablet (corresponding to 1 mg. of equ1valent to 1-5 mg. of KOH unt1l there 1s av1sual color KOH) the solution was red, indicating a neutralization Changc' number between 74 and 5. An article of manufacture useful for determlnrng The following tabulation Shows a comparisen between the neutralization number of mineral 011s, a tablet of the determination of the neutralization number of some an f i a1 hYdmCaYPOH aflmlxed with mineral Oils according to German method DIN 51,558 an alkali metal nltrophenate having d1ssoc1at1on constants and the determination of the neutralization number acof from n integral mult1ple of cording to the method of the present invention and with imounts stolchlomemcany eqmvalent to of tablets containing phenanthrene as carrier material and sodium m-nitrophenate as active material in such a quan- The article of F m} 5 Wherem the hydrocarbon 1s m th h bl correspond to 5 1 mg of KOH, phenanthrene and the nitrophenate 1s sodium m-mtrohalf tablets of the latter type of tablets also being used pheflatein some instances. 7. An article of manufacture useful for determming Determination with Tablets Neutralizag gg Neutraltion Number Test N0. 011 Vessel ization According Filled number to DIN up to Corre- Corre- 51,558 Mark, sponding spending ml. to 5 mg to 1 mg. of KOH of KOH 1 used steam-turbine 5.5 5.5 1.0-1.1 1.06 11 2 0.5 10-105 1 .06 11 0.5 under 0.05 0.03

0 4 used steam-turbine 5.5 2 0.2-0.4 0.42

01 5 50.. 11 4.5 0.4-0.45 0.42 do 11 4 0.3-0.4 0.36 fresh steam-turbine 11 0.5 under 0.05 0.03

01 user} steam-turbine 5.5 3 0.4-0.6 0.65

01 do 11 1 2 0.0-0.7 0.65 used hydraulic oil-.. 11 2.5 0.2-0.25 0.22 do 11 1.5 01-015 0.13 5.5 4 0.6-0.8 0.84 11 4 0.5-0.9 0. 84 11 4.5 0.4-0.45 0.44 5.5 1 about 0.2 0.18 11 2 0.1-0.2 0.18 5.5 4 0.6-0.8 0. 5.5 a 7.4-7.6 7.5 5.5 5.0-6.0 5.0 0 5.5 4 5.6-5.8 5.6 used hardening oil. 5.5 4 0.6-0.8 0. 68 used motor oil 11 8 0.7-0.8 0.7 used hardening oil... 11 2 3 1.2-1.3 1.23 24 fresh machine oil 5.5 3 0.4-0.6 0.49

distillate.

11 5 0.4-0.5 0.49 5.5 8.5 1.6-1.7 1.50 5.5 2 2.2-2.4 2.5 sion oil. 28 used motor oil 5.5 2 0.2-0.4 0.28 29 fresh cuttmgoil 11 4 0.3-0.4 0.30

The method described can be used both with mineral the neutralization number of mineral oil, a tablet of phenoils and with fatty oils and synthetic oils and mixtures 70 anthrene admixed with sodium m-nitrophenate in an of oils. The specific gravity of the oil to be tested should, amount stoichiometrically equivalent to 1 mg. of KOH. of course, invariably be considered when measuring the 8. An article of manufacture useful for determining oil sample. the neutralization number of mineral oil, a tablet of phen- We claim as our invention: anthrene admixed with sodium m-nitrophenate in an 1. A method of determining the neutralization number amount stoichiometrically equivalent to 5 mg. of KOH.

of mineral oils which are subject to contamination with.

(References 011 following page) References Cited in he file of this patent UNITED STATES PATENTS Guernsey Jan. 12, 1932 OTHER REFERENCES Whitmore: Organic Chemistry, D. Van Nostrand 6 Co., Inc., 250 Fourth Ave., New York, N.Y., 1937, pages 781-782.

ASTM Standards on Petroleum Products and Lubricants, published by the American Society for Testing 5 Materials, 1916 Race St., Philadelphia 3, Pa., 1959 (D974-58T), pages 450454. 

1. A METHOD OF DETERMINING THE NEUTRALIZATION NUMBER OF MINERAL OILS WHICH ARE SUBJECTED TO CONTAMINATION WITH ACIDIC SUBSTANCES AND CONCOMITANT DETERIORATION WHICH COMPRISES MEASURING A SAMPLE OF THE OIL AND DISSOLVING IT IN AN ALCOHOL-BENZENE SOLUTION CONTAINING AN INDICATOR AND DISSOLVING THEREIN THE NUMBER OF TABLETS HAVING DISSOCIATION CONSTANTS OF FROM 5.3X10-9 TO 10X10-9 OF ALKALI NITROPHENATE UNTIL THERE IS A VISUAL COLOR CHANGE. 